850 (1973) Mercury Impeller Removal.

[Bender013]

Hi,

Just pick up a 17' boat with a 1973 850 Mercury outboard. Looking for a manual on how to take the lower unit off if I need to. The telltale has a avarage stream of water - not real strong but does flow. Just want to know how to remove and what to watch out for if I need to replace the impeller.

 

[Chris1956]

Re: 850 (1973) Mercury Impeller Removal.

That motor is a standard Merc. Most any Merc Service Manual will give instructions to remove the gearcase, and R&R the waterpump.

Since those waterpump impellers are critical to keep the motor from cooking itself, I would recommend you get a manual and do the repair, before using the motor. A low speed test of the motor is likely OK, to establish that the motor and gears work OK.

 

[egclassic]

Re: 850 (1973) Mercury Impeller Removal.

I have the same motor. The "pee stream" on mine is not very strong either, and I have replaced the impeller. On my 35hp Merc, the water blasts out of the tell tale, maybe shorter distance to travel.

 

[Gomer50]

Re: 850 (1973) Mercury Impeller Removal.

I have the 1972 800 model and my advice is to make darn sure that you get a good stream out of your tell tale,the top cylinder will not be cooled enough and will cause problems.Too take the lower unit off,
1)Put your motor in forward gear.
2) There are three bolts 2 on each side and 1 on the front
3) There 2 more under the cavitation plate
4) 1 trim tab bolt and one underneath that.
5) Wiggle pull and sometimes you can tap it with a rubber mallet and she should drop down.
Good Luck...

 

[emckelvy]

Re: 850 (1973) Mercury Impeller Removal.

One thought about impeller replacement...........if you don't know when it was last replaced, do it! Otherwise you'll stand a strong chance of burning up your powerhead and turning your motor into a boat anchor! Definitely cheaper to invest $22 for a new 47-89984T4 impeller, a few bucks for some pump gaskets and maybe a pump plate (only if it's worn). Also a new O-ring for the driveshaft (seals the splines where it enters the crankshaft).

It's a relatively easy job, the instructions the O.P. gave are great. Just be sure to use some waterproof boat bearing grease or Mercury Corrosion-Preventative grease on the driveshaft and shift shaft splines (but wipe any excess off the tops), also on the bolts/studs so they don't seize up in the future.

And very very important not to move the shifter or shift shaft in the lower unit, after removal. This'll ensure that she still shifts correctly after you reassemble. Take a look at the postings here everyday, you'll see that getting this messed-up is a real common problem. And easy to prevent if you're careful.

Check out the parts diagrams at www.boats.net www.crowleymarine.com or www.mercruiserparts.com for lotsa good info on your motor.

HTH & Happy Boating........ed

 

[Chris1956]

Re: 850 (1973) Mercury Impeller Removal.

I recommend you put the motor in neutral, prior to dropping the gearcase. it will be much easier to align the shift shafts for reassembly. Also remove the wrap cowl and top cowl, so you may turn the flywheel by hand when installing gearcase. You need to line up driveshaft splines with the crankshaft splines. Grease all splines, prior to reassembly...

 

[crazymac-680]

Re: 850 (1973) Mercury Impeller Removal.

Its a pretty easy job. I dont own an manual and have the same engine as you. I got lower unit off, impeller changed and back on in about an hour. I've never done the job before. I then realised that things never went as smoothly as I thought. My shift shaft had come out of my gearbox meaning I couldn't change gear. It shouldn't have happened because inside the gearbox have been a clip, so hopefully wont happen to you. I wouldn't use even a rubber mallet to loosen the lower unit. The alloy is very soft.
The bolts on the left and the right that hold the lower unit on can be used as jacking points. I put a spanner at the top of these bolts and then screwed the bolts off. Effectivly pushing the lower unit away from the leg
Hopefully this makes a little bit of sense.
I also have a fair weak pee stream. Fitting the new impeller didn't change this but it did give me peace of mind.
I bought the impeller kit complete from ribmarineparts. About ?52 with postage.